Octylphenol formaldehyde resin with low free formaldehyde content and preparation method thereof

Abstract

The invention relates to the technical field of polymer synthesis, in particular to octyl phenol formaldehyde resin with low free formaldehyde content and a preparation method thereof.The method comprises the steps that firstly, beta-cyclodextrin and para aminobenzoic acid are mixed in an aqueous solution, and a pre-complex of an inclusion structure is prepared; then octyl phenol and formaldehyde are subjected to a condensation polymerization reaction in the presence of an acid catalyst to obtain a prepolymer, and the key point is that the obtained acid prepolymer is firstly subjected to pH adjustment to be weakly acidic or neutral, then the pre-complex and furfuryl alcohol are added for a composite modification reaction, and finally the product is obtained through dehydration. The pH adjusting step effectively activates the formaldehyde capture activity of amino in the pre-complex and inhibits self-polymerization of furfuryl alcohol, efficient in-situ chemical capture of free formaldehyde and synchronous toughening of a resin network are achieved through cooperation of the two steps, the content of free formaldehyde in the prepared resin is not higher than 0.05%, the content of free octyl phenol is not higher than 0.1%, and the prepared resin has the advantages of being good in mechanical property, good in mechanical property and the like. The toughness, the heat stability and the aging resistance are higher, and the comprehensive performance is excellent.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, and in particular to an octylphenol formaldehyde resin with low free formaldehyde content and its preparation method. Background Technology

[0002] Octylphenol formaldehyde resin is an important type of thermoplastic alkylphenol formaldehyde resin. Due to its good compatibility with rubber matrix, excellent tackifying effect, and ability to improve the processing performance of rubber compounds and the mechanical properties of vulcanized rubber, it is widely used as a tackifying resin in high-performance rubber products such as radial tires, conveyor belts, and rubber shock-absorbing products. Traditional octylphenol formaldehyde resin is usually prepared by polycondensation reaction of p-tert-octylphenol and formaldehyde under acidic catalyst. However, this polycondensation reaction is a reversible process and it is difficult to completely react, which inevitably leads to the presence of unreacted free formaldehyde and free octylphenol in the final resin product.

[0003] With increasingly stringent global environmental regulations and rising consumer demands for health and safety, the development of octylphenol formaldehyde resin with low or even ultra-low free formaldehyde has become an inevitable trend in the industry. Reducing the free formaldehyde content in the resin not only helps to reduce its harm to the environment and operators during production and use, but also meets the prerequisite for manufacturing high-end green rubber products.

[0004] While there are reports of using copolymerization modification to reduce free formaldehyde in existing technologies, there is often a contradiction between the modification effect and the basic properties of the resin. For example, simply adding formaldehyde scavengers may limit their reactivity in a strongly acidic polycondensation environment or have poor compatibility with the resin, resulting in uneven modification and even affecting the resin's thickening effect and thermal stability. In addition, some modification methods are complex and require harsh conditions, which are not conducive to industrial production and cost control. Therefore, developing a new method that can efficiently capture free formaldehyde in situ under mild conditions without damaging or even improving the overall performance of the resin remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides an octylphenol formaldehyde resin with low free formaldehyde content and a method for its preparation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a low-free-formaldehyde octylphenol formaldehyde resin includes the following steps:

[0008] S1. β-cyclodextrin and p-aminobenzoic acid are mixed in a solvent to prepare a precomplex;

[0009] S2. Under catalytic conditions, octylphenol and formaldehyde undergo a polycondensation reaction to obtain an acidic octylphenol formaldehyde resin prepolymer.

[0010] S3. A composite modification reaction is carried out on the prepolymer obtained in S2, which includes: first adjusting the system to pH 5.0-7.0 to activate the formaldehyde-capturing activity of the amino group on p-aminobenzoic acid in the precomposite and inhibit the self-polymerization of furfuryl alcohol; then adding the precomposite obtained in S1 and furfuryl alcohol, and reacting at 65-80℃ for 2-4 hours. Formaldehyde is captured in situ through the chemical bonding between the amino group and formaldehyde in the precomposite, and the rigid structure of β-cyclodextrin and the flexible segments of furfuryl alcohol are used to synergistically construct an interpenetrating network to achieve simultaneous toughening of the resin.

[0011] S4. After the reaction is completed, the product is dehydrated and discharged to obtain the octylphenol formaldehyde resin with low free formaldehyde.

[0012] In step S1, the mass ratio of β-cyclodextrin to p-aminobenzoic acid is 1:0.5-1:2, the solvent is water, and its mass is 3-10 times the total mass of β-cyclodextrin and p-aminobenzoic acid. The mixing temperature is 40-70℃, the stirring speed is 300-600 rpm, and the mixing time is 30-90 min.

[0013] Furthermore, in S2, the molar ratio of octylphenol to formaldehyde is 1:1.0 to 1:1.8, the catalyst is an organic acid or Lewis acid, and its mass is 0.5%-2.5% of the mass of octylphenol. The organic acid is one of oxalic acid, citric acid or glacial acetic acid, and the Lewis acid is zinc chloride or boron trifluoride complex. The catalyst is preferably oxalic acid, and its mass is 1.0%-1.8% of the mass of octylphenol.

[0014] Furthermore, the polycondensation reaction described in S2 is carried out at a temperature of 80-95°C for 1-3 hours, and the reaction endpoint is controlled by monitoring the viscosity or tolerance of the system.

[0015] Furthermore, in S3, the total mass of the precomplex added accounts for 5%-20% of the mass of octylphenol, and the mass of furfuryl alcohol added accounts for 3%-15% of the mass of octylphenol.

[0016] Furthermore, the temperature of the composite modification reaction described in S3 is 65-80℃, and the reaction time is 2-4h.

[0017] Furthermore, the dehydration described in S4 is carried out under reduced pressure dehydration at a temperature of 100-120°C and a vacuum degree of -0.085 to -0.098 MPa until the resin softening point reaches 95-105°C.

[0018] Furthermore, an octylphenol-formaldehyde resin with low free formaldehyde content prepared by the preparation method according to any one of claims 1-6 has a free formaldehyde content of not more than 0.05% and a free octylphenol content of not more than 0.1%.

[0019] Furthermore, the softening point of the low-free-formaldehyde octylphenol formaldehyde resin is 95-105℃.

[0020] Furthermore, the low-free-formaldehyde octylphenol formaldehyde resin is used as a tackifier in rubber compounds, particularly in radial tires, conveyor belts, or rubber shock-absorbing products.

[0021] Furthermore, the octylphenol-formaldehyde resin with low free formaldehyde exhibits a 5% mass loss temperature (Td5%) of not less than 340℃ and an impact strength of not less than 5.0 kJ / m² in thermogravimetric analysis. 2 Furthermore, after heat aging at 125℃ for 168 hours, the increase in free formaldehyde content does not exceed 0.05 percentage points.

[0022] The beneficial effects of this invention are:

[0023] 1. In the technical solution of this invention, the hydrophobic cavity of β-cyclodextrin is encapsulated by the benzene ring of p-aminobenzoic acid, thereby exposing its reactive amino group (-NH2). Under suitable weakly acidic / neutral reaction environment, this amino group can react with free formaldehyde efficiently and specifically to generate a stable chemical bond structure represented by Schiff base (C=N bond), and may further form a more stable cyclic or cross-linked network. This process is a chemical capture that directly and permanently fixes free formaldehyde into the resin system through covalent bonds, rather than physical adsorption. Therefore, the effect is stable and long-lasting, fundamentally and significantly reducing the free formaldehyde content of the resin.

[0024] 2. In the technical solution of this invention, the strongly acidic polycondensation reaction system is precisely adjusted to a weakly acidic / neutral environment. This environment ensures that the amino group on p-aminobenzoic acid is in a highly reactive, deprotonated state, which fully activates its formaldehyde capture ability. At the same time, it effectively inhibits the violent self-polymerization reaction of furfuryl alcohol under strong acid, guiding it to participate more in the copolymerization with the resin prepolymer. This precise control of the reaction environment avoids the deactivation of the modifier or competition from side reactions, ensuring the high efficiency and controllability of the modification process.

[0025] 3. In the technical solution of this invention, the rigid macrocyclic structure of β-cyclodextrin serves as an "anchor point" and "crosslinking hub." Its hydrophobic cavity, through the inclusion effect of the benzene ring of p-aminobenzoic acid, not only improves the compatibility and dispersibility of the modifier in the hydrophobic resin system, but also may significantly increase the local concentration of reactants through the "local enrichment effect," thereby synergistically promoting the formaldehyde capture efficiency. It is uniformly dispersed in the resin network, effectively dispersing stress and hindering crack propagation. At the same time, the flexible methylene ether segment (-CH2-O-CH2-) introduced by furfuryl alcohol through the copolymerization reaction is interwoven in the network, synergistically with β-cyclodextrin to jointly construct a "rigid and flexible" interpenetrating network structure. This dense and stable structure not only enhances the intermolecular forces and improves the thermal stability of the resin, but also exhibits excellent heat aging resistance due to its effective fixation of free small molecules.

[0026] 4. In the technical solution of this invention, formaldehyde capture, network toughening and densification are integrated into a one-step composite modification reaction. The process is simple and efficient, overcoming the defects of low efficiency of traditional post-treatment methods or the influence of compatibility caused by the addition of external capture agents. The resin product obtained successfully solves the problems of high free formaldehyde content, brittle performance and impaired compatibility with rubber of traditional octylphenol formaldehyde resin.

[0027] 5. In the technical solution of the present invention, the carboxyl group (-COOH) in the p-aminobenzoic acid molecule may also participate in the reaction, such as esterification with the phenolic hydroxyl group of the resin network, or reaction with the hydroxymethyl group generated after capturing formaldehyde with its own amino group. These potential further reactions help to form a denser and more stable cross-linked network, which together contribute to the final performance of the resin with low free formaldehyde content, high toughness and excellent thermal stability. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0030] Example 1: Optimization Scheme

[0031] S1: Preparation of the precomplex

[0032] In a 500 mL three-necked flask, add 90 g of deionized water (as a solvent, with a mass of 4.5 times the total mass of β-cyclodextrin and p-aminobenzoic acid), 10.0 g of β-cyclodextrin (β-CD), and 10.0 g of p-aminobenzoic acid (PABA) in sequence (i.e., a mass ratio of 1:1).

[0033] Place the three-necked flask in a constant temperature water bath, turn on the mechanical stirrer, set the stirring speed to 500 rpm, heat to 60°C, and maintain the temperature at this temperature for 60 minutes.

[0034] After the reaction is complete, a clear or slightly turbid solution is obtained, which is the aqueous solution of β-CD / PABA precomplex, for later use.

[0035] S2: Preparation of octylphenol formaldehyde resin prepolymer

[0036] In a 1000 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser and water separator, precisely add 206.0 g of p-tert-octylphenol (molar mass of 206 g / mol), 81.0 g of 37% formaldehyde aqueous solution (equivalent to 30.0 g of pure formaldehyde, with a molar ratio of 1:1.32 to octylphenol), and 2.47 g of oxalic acid (1.2% of the mass of octylphenol) as an acidic catalyst.

[0037] Slowly raise the temperature to 90°C, turn on the stirrer (300 rpm), and begin the polycondensation reaction. Separate the water produced by the reaction through a water separator.

[0038] After the reaction has proceeded for about 2 hours, samples are taken periodically, and the reaction endpoint is monitored using the methanol tolerance method: a small amount of reactant is mixed with methanol at a ratio of 1:3 (volume ratio). If obvious turbidity or opalescence appears, it is considered that the prepolymerization endpoint has been reached, and heating is stopped at this point.

[0039] S3: Composite Modification Reaction

[0040] First, the acidic prepolymer obtained from S2 (at a system temperature of approximately 90°C) undergoes a crucial treatment: it is cooled to 70°C using a water bath, and then a 10% (w / w) sodium hydroxide (NaOH) aqueous solution is slowly added dropwise using a dropping funnel, while monitoring the pH of the system with precision pH paper or a pH meter until the pH value of the system stabilizes at 6.0. This step aims to create the optimal reaction environment for subsequent composite modification: on the one hand, to ensure that the amino group of p-aminobenzoic acid is in a highly reactive, deprotonated state to efficiently capture formaldehyde; on the other hand, to inhibit the vigorous self-polymerization of furfuryl alcohol and guide it to participate in effective copolymerization.

[0041] Subsequently, in the prepolymer system with adjusted pH, under continuous stirring, the entire aqueous solution of the β-CD / PABA precomplex prepared in S1 (containing 10g of β-CD, 10g of PABA, a total mass of 20g, accounting for 9.7% of the mass of octylphenol) and 20.6g of furfuryl alcohol (accounting for 10% of the mass of octylphenol) were slowly added dropwise through a dropping funnel. Under these conditions, the amino group of p-aminobenzoic acid in the precomplex reacted with the free formaldehyde in the system to form a stable chemical bond. At the same time, furfuryl alcohol copolymerized with the resin prepolymer and β-cyclodextrin molecules to synergistically construct a dense and tough interpenetrating network structure.

[0042] The system temperature was maintained at 70℃, and the reaction was continued with stirring for 3 hours. This composite modification process achieved the dual effects of in-situ chemical capture of free formaldehyde and simultaneous toughening and densification of the resin network.

[0043] S4: Post-processing

[0044] After the reaction was completed, the temperature was raised to 110°C and the vacuum pump was turned on to carry out dehydration under reduced pressure at a vacuum of -0.095 MPa. During this process, the softening point of the resin was monitored to control the dehydration endpoint.

[0045] When the softening point (ring and ball method) of the resin reaches 100°C, heating and vacuuming are immediately stopped. The resin is discharged while hot and cooled in a shallow dish to obtain a light yellow, transparent blocky solid resin, which is then crushed and packaged.

[0046] Example 2: High Pre-complex Dosage Scheme

[0047] S1: Preparation of the precomplex

[0048] In a 500 mL three-necked flask, add 108 g of deionized water (as a solvent, with a mass of 4.5 times the total mass of β-cyclodextrin and p-aminobenzoic acid), 12.0 g of β-cyclodextrin (β-CD), and 12.0 g of p-aminobenzoic acid (PABA) in sequence (i.e., a mass ratio of 1:1).

[0049] Place the three-necked flask in a constant temperature water bath, turn on the mechanical stirrer, set the stirring speed to 500 rpm, heat to 60°C, and maintain the temperature at this temperature for 60 minutes.

[0050] After the reaction is complete, a clear or slightly turbid solution is obtained, which is the aqueous solution of β-CD / PABA precomplex, for later use.

[0051] S2: Preparation of octylphenol formaldehyde resin prepolymer

[0052] In a 1000 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser and water separator, precisely add 206.0 g of p-tert-octylphenol, 81.0 g of 37% formaldehyde aqueous solution (molar ratio of formaldehyde to octylphenol 1:1.32), and 2.47 g of oxalic acid (1.2% of the mass of octylphenol) as an acidic catalyst.

[0053] Slowly raise the temperature to 90°C, turn on the stirrer (300 rpm), and begin the polycondensation reaction. Separate the water produced by the reaction through a water separator.

[0054] After the reaction has proceeded for about 2 hours, samples were taken periodically, and the reaction endpoint was monitored using the methanol tolerance method (turbidity appeared when the mixture was 1:3 in volume). Heating was stopped after the endpoint was reached.

[0055] S3: Composite modification reaction (including pH adjustment)

[0056] First, the acidic prepolymer obtained from S2 was cooled to 70°C in a water bath. Then, a 10% (w / w) sodium hydroxide (NaOH) aqueous solution was slowly added dropwise using a dropping funnel. The pH of the system was monitored with precision pH paper or a pH meter while the solution was being added until the pH value of the system stabilized at 6.0. This pH adjustment process activated the amino group capture activity and optimized the reaction pathway of furfuryl alcohol.

[0057] Subsequently, under continuous stirring, the aqueous solution of all the β-CD / PABA precomplex prepared in S1 (containing 12g of β-CD, 12g of PABA, a total mass of 24g, accounting for 11.7% of the mass of octylphenol) and 10.3g of furfuryl alcohol (accounting for 5% of the mass of octylphenol) were slowly added to the prepolymer whose pH value had been adjusted. This process fixes formaldehyde through chemical bonding and strengthens the resin network by utilizing the synergistic effect of rigid β-cyclodextrin and flexible furfuryl alcohol segments.

[0058] Maintain the system temperature at 70℃ and continue stirring the reaction for 3 hours.

[0059] S4: Post-processing

[0060] After the reaction is complete, the temperature is raised to 110°C and the vacuum pump is turned on to perform decompression dehydration at a vacuum of -0.095 MPa.

[0061] When the softening point (ring and ball method) of the resin reaches 99°C, heating and vacuuming are immediately stopped. The resin is discharged while hot and cooled in a shallow dish to obtain a light yellow, transparent blocky solid resin, which is then crushed and packaged.

[0062] Example 3: Low Pre-complex Dosage Scheme

[0063] S1: Preparation of the precomplex

[0064] In a 500 mL three-necked flask, add 72 g of deionized water (4.5 times the total mass of β-cyclodextrin and p-aminobenzoic acid), 8.0 g of β-cyclodextrin (β-CD), and 8.0 g of p-aminobenzoic acid (PABA) in sequence (i.e., a mass ratio of 1:1).

[0065] Place the three-necked flask in a constant temperature water bath, turn on the mechanical stirrer, set the stirring speed to 500 rpm, heat to 60°C, and stir at this temperature for 60 min to obtain an aqueous solution of β-CD / PABA precomplex for later use.

[0066] S2: Preparation of octylphenol formaldehyde resin prepolymer

[0067] In a 1000mL four-necked flask, add 206.0g of p-tert-octylphenol, 81.0g of 37% formaldehyde aqueous solution (molar ratio 1:1.32), and 2.47g of oxalic acid.

[0068] Slowly raise the temperature to 90°C, turn on the stirrer (300 rpm) to carry out the polycondensation reaction, and separate the water through the water separator.

[0069] After about 2 hours of reaction, the endpoint was reached by monitoring the methanol tolerance method, and heating was stopped.

[0070] S3: Composite modification reaction (including pH adjustment)

[0071] First, the prepolymer obtained from S2 was cooled to 65°C, and the pH of the system was adjusted to 5.5 with a 10% NaOH aqueous solution. This slightly acidic environment provided stable conditions for the modification reaction.

[0072] Subsequently, under continuous stirring, the entire aqueous solution of the precomplex prepared in S1 (containing 8g of β-CD, 8g of PABA, a total mass of 16g, accounting for 7.8% of octylphenol) and 24.7g of furfuryl alcohol (accounting for 12% of octylphenol) were added. Under these conditions, the formaldehyde capture and network toughening reactions proceeded synergistically.

[0073] Maintain the system temperature at 65℃ and continue stirring the reaction for 4 hours.

[0074] S4: Post-processing

[0075] After the reaction was completed, the product was dehydrated under reduced pressure at 110℃ and -0.095MPa.

[0076] When the resin softening point reaches 103℃, it is discharged and cooled to obtain a light yellow transparent solid resin.

[0077] Comparative Example 1: Traditional octylphenol formaldehyde resin

[0078] S2: Preparation of octylphenol formaldehyde resin prepolymer

[0079] In a 1000mL four-necked flask, precisely add 206.0g of p-tert-octylphenol, 81.0g of 37% formaldehyde aqueous solution (molar ratio 1:1.32), and 2.47g of oxalic acid catalyst.

[0080] Slowly raise the temperature to 90°C, turn on the stirrer (300 rpm) to carry out the condensation reaction, and separate the water generated by the reaction through a water separator.

[0081] The reaction proceeded for approximately 2 hours. Once the tolerance was monitored and the endpoint was reached, heating was stopped, and no further modification was performed.

[0082] S4: Post-processing

[0083] The obtained prepolymer was directly subjected to dehydration under reduced pressure, heated to 110℃, and dehydrated under a vacuum of -0.095MPa.

[0084] When the resin's softening point reaches 97°C, heating and vacuuming are stopped, and the resin is discharged while still hot to obtain a brownish-red, brittle, transparent solid resin.

[0085] Comparative Example 2: Contains modifier but no pH adjustment

[0086] S1: Preparation of the precomplex

[0087] As in Example 1, an aqueous solution of β-CD / PABA precomplex (containing 10g of β-CD and 10g of PABA) was prepared for later use.

[0088] S2: Preparation of octylphenol formaldehyde resin prepolymer

[0089] As in Example 1, an acidic octylphenol formaldehyde resin prepolymer was prepared.

[0090] S3: Composite modification reaction (without pH adjustment)

[0091] The acidic prepolymer obtained from S2 was directly cooled to 70°C (without pH adjustment, at which point the pH value of the system was approximately 2.5). Under these strongly acidic conditions, the amino group of p-aminobenzoic acid was protonated and deactivated, and furfuryl alcohol was prone to self-polymerization.

[0092] Subsequently, under these strongly acidic conditions, the entire aqueous solution of the precomplex prepared by S1 and 20.6 g of furfuryl alcohol were directly added.

[0093] The system temperature was maintained at 70℃, and the reaction was continued with stirring for 3 hours. Due to the lack of key reaction conditions, the modifier could not play an effective role.

[0094] S4: Post-processing

[0095] After the reaction was completed, dehydration under reduced pressure was carried out as usual (110℃, -0.095MPa).

[0096] When the resin softening point reaches 98℃, the material is discharged to obtain a brownish-red, slightly turbid solid resin containing fine particles.

[0097] Comparative Example 3: Modification with furfuryl alcohol only (without pre-complex)

[0098] As in Example 1, an acidic octylphenol formaldehyde resin prepolymer was prepared.

[0099] S3: Composite modification reaction (including pH adjustment, but without pre-complex)

[0100] First, the prepolymer obtained from S2 was cooled to 70°C, and the pH of the system was adjusted to 6.0 with a 10% NaOH aqueous solution. This environment is conducive to the furfuryl alcohol reaction.

[0101] Subsequently, only 20.6g of furfuryl alcohol (accounting for 10% of octylphenol) was added to the system without any pre-complex. Due to the lack of synergistic effect of the pre-complex, the formaldehyde capture efficiency and network enhancement effect were limited.

[0102] Maintain the system temperature at 70℃ and continue stirring the reaction for 3 hours.

[0103] S4: Post-processing

[0104] After the reaction was completed, dehydration was carried out under reduced pressure (110℃, -0.095MPa).

[0105] When the resin softening point reaches 102°C, it is discharged to obtain a light yellow transparent solid resin, which has an appearance similar to the product of Example 1.

[0106] Effect verification example

[0107] The octylphenol formaldehyde resins prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to the following performance tests, and the test methods and standards are as follows:

[0108] Free formaldehyde content: Determined according to GB / T 14074-2013 Test methods for adhesives and resins for wood industry or by acetylacetone spectrophotometry.

[0109] Free octylphenol content: determined by gas chromatography (GC).

[0110] Softening point: The determination was made in accordance with GB / T 4507-2014 Determination of softening point of asphalt (ring and ball method).

[0111] Thermal stability (thermogravimetric analysis, TGA): The temperature Td5% at which 5% mass loss occurs is recorded under a nitrogen atmosphere by heating from room temperature to 600°C at a rate of 10°C / min to evaluate the thermal stability of the resin.

[0112] Toughness (impact strength): The resin is pressed into standard specimens, and its impact strength is determined in accordance with GB / T 1043.1-2008 Determination of impact properties of simply supported plastic beams to evaluate the brittleness / toughness of the resin.

[0113] Functional durability (heat aging resistance): The resin sample was aged in a 125℃ forced-air drying oven for 168 hours (equivalent to heat aging under long-term use conditions), and then its free formaldehyde content was measured again. The long-term stability of the resin was evaluated by the increase in free formaldehyde after aging.

[0114] The test results of mechanical properties and thermal stability are shown in Table 1, and the test results of free content and heat aging resistance are shown in Table 2.

[0115] Table 1. Test results of mechanical properties and thermal stability of Examples 1-3 and Comparative Examples 1-3

[0116] sample Softening point (°C) <![CDATA[Impact strength (kJ / m 2 )]]> 5% thermal weight loss at temperature Td (°C) Example 1 100 5.8 348 Example 2 99 6.5 341 Example 3 103 5.2 355 Comparative Example 1 97 2.1 325 Comparative Example 2 98 2.5 318 Comparative Example 3 102 4.5 338

[0117] Table 2. Free content and heat aging resistance test results of Examples 1-3 and Comparative Examples 1-3

[0118] sample Free formaldehyde (%) Free octylphenol (%) Free formaldehyde after aging (%) Formaldehyde increase (percentage points) Example 1 0.03 0.05 0.07 +0.04 Example 2 0.02 0.06 0.05 +0.03 Example 3 0.04 0.04 0.09 +0.05 Comparative Example 1 0.38 0.25 0.52 +0.14 Comparative Example 2 0.35 0.08 0.61 +0.26 Comparative Example 3 0.15 0.07 0.28 +0.13

[0119] As shown in Tables 1 and 2, the octylphenol formaldehyde resins prepared in Examples 1-3 of this invention are significantly superior to the comparative examples in terms of key performance.

[0120] The initial free formaldehyde content (0.02-0.04%) in Examples 1-3 was much lower than that in Comparative Example 1 (0.38%) and Comparative Example 2 (0.35%), demonstrating that the synergistic modification system of "pre-composite + furfuryl alcohol" at a suitable pH can efficiently achieve in-situ capture of free formaldehyde. After thermal aging, the formaldehyde increase in the examples (+0.03 to +0.05 percentage points) was much smaller than that in Comparative Example 1 (+0.14) and Comparative Example 2 (+0.26), indicating that the resin of the present invention has superior heat aging resistance, stable structure, and is not easily decomposed and releases formaldehyde.

[0121] Comparative Example 2 (with modifier but no pH adjustment) showed similar performance to Comparative Example 1 (traditional resin), and its formaldehyde content increased the most after thermal aging. This strongly demonstrates that "adjusting the pH to weakly acidic / neutral (S2a step)" is a necessary condition for activating the formaldehyde-capturing activity of the amino group of p-aminobenzoic acid in the precomposite. In a strongly acidic environment, the amino group is protonated and deactivated, the modifier cannot play a role, and may even cause structural defects due to the violent self-polymerization of furfuryl alcohol.

[0122] Although the free formaldehyde (0.15%) and toughness (4.5 kJ / m²) of Comparative Example 3 (using furfuryl alcohol only) were better than those of the traditional resin, they were both inferior to those of Example 1 (0.03%, 5.8 kJ / m²). This indicates that there is a significant synergistic effect between the β-cyclodextrin / p-aminobenzoic acid precomplex and furfuryl alcohol. The cavity structure of β-cyclodextrin may promote the reaction through inclusion, and its own polyhydroxy system and the introduction of PABA may enhance the intermolecular forces or form an interpenetrating network, thus jointly contributing to the toughening effect and thermal stability improvement of the resin.

[0123] In summary, this invention, through innovative "pre-composite" design and key "pH adjustment" steps, successfully prepared an octylphenol formaldehyde resin with extremely low free formaldehyde content, good toughness, and high thermal stability. Its comprehensive performance is significantly superior to traditional processes and other modification methods, meeting the dual requirements of environmental protection and performance in high-end application fields.

[0124] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0125] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-free-formaldehyde octylphenol formaldehyde resin, characterized in that, Includes the following steps: S1. β-cyclodextrin and p-aminobenzoic acid are mixed in a solvent to prepare a precomplex; S2. Under catalytic conditions, octylphenol and formaldehyde undergo a polycondensation reaction to obtain an acidic octylphenol formaldehyde resin prepolymer. S3. A composite modification reaction is carried out on the prepolymer obtained in S2, which includes: first adjusting the system to pH 5.0-7.0, then adding the precomposite obtained in S1 and furfuryl alcohol, and reacting at 65-80℃ for 2-4 hours. S4. After the reaction is completed, the product is dehydrated and discharged to obtain the octylphenol formaldehyde resin with low free formaldehyde. In step S1, the mass ratio of β-cyclodextrin to p-aminobenzoic acid is 1:0.5-1:2, the solvent is water, and its mass is 3-10 times the total mass of β-cyclodextrin and p-aminobenzoic acid. The mixing temperature is 40-70℃, the stirring speed is 300-600 rpm, and the mixing time is 30-90 min.

2. The method for preparing a low-free-formaldehyde octylphenol formaldehyde resin according to claim 1, characterized in that, In S2, the molar ratio of octylphenol to formaldehyde is 1:1.0 to 1:1.8, the catalyst is an organic acid or Lewis acid, and its mass is 0.5%-2.5% of the mass of octylphenol. The organic acid is one of oxalic acid, citric acid or glacial acetic acid, and the Lewis acid is zinc chloride or boron trifluoride complex. The catalyst is preferably oxalic acid, and its mass is 1.0%-1.8% of the mass of octylphenol.

3. The method for preparing a low-free-formaldehyde octylphenol formaldehyde resin according to claim 1, characterized in that, The polycondensation reaction described in S2 is carried out at a temperature of 80-95℃ for 1-3 hours, and the reaction endpoint is controlled by monitoring the viscosity or tolerance of the system.

4. The method for preparing a low-free-formaldehyde octylphenol formaldehyde resin according to claim 1, characterized in that, In S3, the total mass of the precomplex is 5%-20% of the mass of octylphenol, and the mass of furfuryl alcohol is 3%-15% of the mass of octylphenol.

5. The method for preparing a low-free-formaldehyde octylphenol formaldehyde resin according to claim 1, characterized in that, The temperature of the composite modification reaction described in S3 is 65-80℃, and the reaction time is 2-4h.

6. The method for preparing a low-free-formaldehyde octylphenol formaldehyde resin according to claim 1, characterized in that, The dehydration described in S4 is carried out under reduced pressure dehydration at a temperature of 100-120℃ and a vacuum degree of -0.085 to -0.098MPa until the resin softening point reaches 95-105℃.

7. An octylphenol-formaldehyde resin with low free formaldehyde content prepared by the preparation method according to any one of claims 1-6, characterized in that, Its free formaldehyde content is no higher than 0.05%, and its free octylphenol content is no higher than 0.1%.

8. The octylphenol-formaldehyde resin with low free formaldehyde content according to claim 7, characterized in that, Its softening point is 95-105℃.

9. The octylphenol-formaldehyde resin with low free formaldehyde content according to claim 7, characterized in that, It is used as a tackifier in rubber compounds, especially in radial tires, conveyor belts, or rubber shock absorbers.

10. The low-free-formaldehyde octylphenol formaldehyde resin according to any one of claims 7-9, characterized in that, In thermogravimetric analysis, its 5% mass loss temperature (Td5%) is not lower than 340℃, and its impact strength is not lower than 5.0 kJ / m. 2 Furthermore, after heat aging at 125℃ for 168 hours, the increase in free formaldehyde content does not exceed 0.05 percentage points.